This invention relates to the control of engine valves associated with the combustion chamber of an internal combustion engine. In particular, the present invention is directed to an apparatus for controlling the seating of engine valves.
Engine combustion chamber valves, such as intake and exhaust valves, are almost universally of a poppet type. These engine valves are typically spring loaded toward a valve closed position. A number of means exist for opening such valves, including hydraulic pressure. In many systems, hydraulic pressure acts on an actuator piston within a housing or cylinder. The piston may be operatively connected to the valve stem of an engine valve. In response to hydraulic pressure on the top of the piston, the piston translates downward, forcing the engine valve open against the force of a valve spring, opening the engine valve. This hydraulic piston arrangement is commonly referred to as a hydraulic actuator.
A variety of systems exist to regulate the timing of engine valve opening by controlling the hydraulic pressure within the actuator at the top of the actuator piston. These systems include xe2x80x9ccommon railxe2x80x9d systems in which a solenoid control valve, or other valve, opens a path from a source of high pressure fluid to the top of the slave piston at precisely timed instants. One such common rail system is described in Cosma et al., U.S. Pat. No. 5,619,964, assigned to the assignee of the present application.
Another type of system for applying hydraulic pressure to the actuator piston is a hydraulically linked master and slave piston arrangement. In such systems, a cam or other device causes motion of a master piston. Master piston motion is transferred to the actuator (xe2x80x9cslavexe2x80x9d) piston by means of the hydraulic link between the two pistons. The motion of the slave piston, in relation to the basic cam motion imparted to the master piston, may be modified by draining and filling fluid from the hydraulic link at precise times. In this way, only selected portions of the cam-driven motion may be transferred to the slave piston. These systems are sometimes therefore called xe2x80x9clost motionxe2x80x9d systems. One such lost motion system is described in Hu, U.S. Pat. No. 5,537,976, assigned to the assignee of the present application.
Engine valves are required to open and close very quickly, therefore the valve spring is typically very stiff. When the valve closes, it impacts the valve seat at a velocity that can create forces which may eventually erode the valve or the valve seat or even fracture or break the valve. In mechanical valve actuation systems that use a valve lifter to follow a cam profile, the cam lobe shape provides built-in valve-closing velocity control. In common rail hydraulically actuated valve assemblies, however, there is no cam to self-dampen the closing velocity of an engine valve. Likewise, in hydraulic lost motion systems, a rapid draining of fluid from the hydraulic link between the master and slave pistons may allow an engine valve to xe2x80x9cfree fallxe2x80x9d and seat with an unacceptably high velocity.
As a result, in engine valve and cylinder head design, there is a need to limit valve seating velocities. With hydraulically actuated systems, however, this need for restriction is in conflict with the need for unrestricted valve opening rates. Some attempts have been made to solve the problem by providing separate fill and drain ports. U.S. Pat. No. 5,577,468 discloses a system for limiting valve seating velocity, however, the system disclosed is both costly and inaccurate. Other existing methods for controlling engine valve seating velocity do so for the entire range of valve closing. These methods may cause excessive valve closing variations. Existing systems also fail to accommodate the need for adjustments due to variations in engine valve lash between cylinders.
In addition to excessive valve closing speed, piston overtravel can also cause severe engine damage. It is therefore necessary, to precisely control and limit the return stroke of the engine valve and the actuator piston during engine operation. There are several methods of controlling piston stroke: mechanical stops, mechanisms that cut off the flow of fluid to the piston, and mechanisms that apply high pressure oil to the backside of the piston. Each of these designs, however, have shortcomings. Mechanical stops have durability problems unless seating velocity is controlled. Systems that cut off the oil supply may allow overtravel due to the formation of vapor or the evolution of gas bubbles. Systems that bleed high pressure oil behind the piston place an excessive load on the oil pump.
Accordingly, there is a need for a simple and effective stroke-limiting design that is fail-safe. For mechanical stop methods of stroke-limiting, there is a particular need for a design that reduces the risk of damage to the stops. Furthermore, existing systems do not fill the need for valve seating velocity control which allows free, unrestricted return of the engine valve for a set distance and restricted, controlled return as the valve approaches the valve seat.
The present invention meets the aforementioned needs and provides other benefits as well.
It is therefore an object of the present invention to provide a hydraulic engine valve control system which allows free valve return over the majority of the valve""s return distance, and provides velocity control over a limited range of the valve""s travel just prior to seating.
A further object of the present invention is to provide faster, more consistent controlled valve seating.
It is a further object of the present invention to provide a method of free valve return with controlled seating velocity.
Another object of the present invention is to provide an adjustable range over which valve seating velocity is controlled.
It is another object of the present invention to provide an engine valve actuator which allows free, unrestricted opening of an engine valve.
Still another object of the present invention is to provide a means for adjusting, either manually or automatically, an engine valve hydraulic actuation system for variations in engine valve height or lash.
It is also an object of the present invention to provide an improved apparatus for limiting the stroke of the actuator piston.
It is another object of the present invention to provide a piston stroke-limiting means that is fail-safe and low-cost.
It is another object of the present invention to provide slave piston stroke-limiting without a separate stroke-controlling piston.
It is another object of the present invention to provide slave piston stroke-limiting means comprising at least one fixed mechanical stop.
It is another object of the present invention to provide a hydraulic damper that controls the valve seating velocity and thereby reduces damage to the mechanical stop(s).
Additional objects and advantages of the invention are set forth, in part, in the description which follows and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention.
In response to this challenge, applicants have developed an innovative, economical apparatus for controlling the seating velocity of an engine valve. The present invention includes a hydraulic valve actuator for operating an engine valve comprising: an actuator housing; an actuator piston having upper and lower ends, wherein the piston is reciprocally disposed within the housing and is adapted to be moved upward and downward in response to hydraulic pressure; the lower end of the actuator piston is operatively connected to the engine valve so that the engine valve opens when the actuator piston is displaced downward in response to hydraulic pressure upon the upper end, and when the hydraulic pressure is removed from the upper end the actuator piston returns upward and the engine valve shuts; a feed and drain passage in the housing to allow hydraulic fluid to move to and from the upper end of the actuator piston; and a control element disposed within the actuator housing, wherein the control element provides a restriction in hydraulic fluid flow during a portion of the return stroke of the actuator piston thereby limiting the velocity of the actuator piston. The control element may be a disc which includes a central orifice to restrict fluid flow. The disc may include a plurality of orifices to restrict fluid flow.
The actuator piston may include longitudinal and transverse passages which allow fluid to move from the feed and drain passage to the upper end of the piston. The longitudinal passage may include an upper fluid chamber area at the upper end of the actuator piston, and the control element may be disposed within the upper fluid chamber. The actuator piston may further include a protruding exterior annular ring located above the transverse passage and below the upper fluid chamber.
The hydraulic actuator may include a means for adjusting for engine valve lash. The means for adjusting for engine valve lash may comprise: an adjustable sleeve disposed between the actuator piston and the housing and a lash adjustment screw threaded into the housing and contacting the sleeve for adjusting the position of the adjusting sleeve within the housing. Alternatively, the means for adjusting for engine valve lash may comprise: a lash piston disposed reciprocally within the lower end of the actuator piston; a lash compression spring disposed above the lash piston for biasing the lash piston toward the engine valve; and a lash adjustment chamber located within the actuator piston above the lash piston for establishing an hydraulic link between the actuator piston and the lash piston. The actuator piston may further include an internal lower vertical passage for connecting the lash adjustment chamber with the feed and drain passage. The means for adjusting for engine valve lash may further include a check valve between the lower vertical passage and the lash adjustment chamber and wherein the check valve only permits flow into the chamber from the lower vertical passage.
The hydraulic actuator may also comprise: a pin; a pin body; and a piston body; wherein the pin is reciprocally disposed within the pin body and the pin body is disposed within and fixed to the piston body, and the piston body is reciprocally disposed within the housing. The pin body may extend downward from the piston body and be operatively connected to the engine valve. The pin may be biased upward away from the engine valve. The piston body may further include a longitudinal passage and an transverse passage and the pin may extend through the longitudinal passage at the upper end of the piston body. The pin may include a large diameter section so that during the return stroke of the actuator piston the large diameter section of the pin contacts the housing and is forced into the longitudinal passage creating a flow restriction and slowing the velocity of the actuator piston. Alternatively, the pin may include a longitudinal passage and an upper and lower orifice connecting the longitudinal passage to the exterior of the pin. The pin may also include a large diameter section so that during the return stroke of the actuator piston the large diameter section of the pin contacts the housing and is forced into the longitudinal passage substantially cutting off the flow of hydraulic fluid between the piston body and the pin so that fluid flows through the upper and lower orifices thereby creating a flow restriction and slowing the velocity of the actuator piston.
In an alternative embodiment the hydraulic actuator of the present invention the control element is a seating piston reciprocally disposed partially within the longitudinal passage at the upper end of the actuator piston. The seating piston may include a vertical passage through which fluid flows from the upper fluid chamber to the feed and drain passage. The actuator may further include a spring disposed in the longitudinal passage below the seating piston, wherein the spring biases the seating piston upward away from the engine valve. The seating piston may include a notch at its upper end so that during the return stroke of the actuator piston when the seating piston contacts the housing and is forced downward further into the longitudinal passage a restricted flow path is established from the upper fluid chamber through the notch and the vertical passage to the feed and drain passage.
A further embodiment of the present invention includes a hydraulic valve actuator for operating an engine valve comprising: an actuator housing; an actuator piston having upper and lower ends, wherein the piston is reciprocally disposed within the housing and is adapted to be moved upward and downward in response to hydraulic pressure; the lower end of the actuator piston is operatively connected to the engine valve so that the engine valve opens when the actuator piston is displaced downward in response to hydraulic pressure upon the upper end, and when the hydraulic pressure is removed from the upper end the actuator piston returns upward and the engine valve shuts; a feed and drain passage in the housing to allow hydraulic fluid to move to and from the upper end of the actuator piston; and a snubber plunger disposed within the actuator housing above the actuator piston, wherein the snubber plunger provides a restriction in hydraulic fluid flow during a portion of the return stroke of the actuator piston thereby limiting the velocity of the actuator piston. The snubber plunger may be reciprocally disposed within a plunger housing and may be biased downward toward the actuator piston by a spring. The actuator may fuher include a plunger chamber located above the snubber plunger. The snubber plunger may also include a vertical passage providing a flow path from the plunger chamber through the snubber plunger. The snubber plunger may be disposed within the plunger housing so that during the upward motion of the snubber plunger fluid may flow out of the plunger chamber through the clearance between the snubber plunger and the plunger housing. The snubber plunger may include a vertical passage and a horizontal passage providing a flow path from the plunger chamber through the snubber plunger.
The present invention may also be a hydraulic valve actuator for operating an engine valve comprising: an actuator housing having a vertically aligned central bore; an actuator piston having upper and lower ends, wherein the piston is reciprocally disposed within the central bore and is adapted to be moved upward and downward in response to hydraulic pressure; the lower end of the actuator piston is operatively connected to the engine valve so that the engine valve opens when the actuator piston is displaced downward in response to hydraulic pressure upon the upper end, and when the hydraulic pressure is removed from the upper end the actuator piston returns upward and the engine valve shuts; an end cap located above the actuator piston position to seal off the upper end of the central bore and retain the actuator piston; a feed and drain passage in the housing to allow hydraulic fluid to move to and from the upper end of the actuator piston; and a dampening assembly comprising a cavity on the downward side of the end cap, wherein the cavity is capable of receiving the upper end of the actuator piston so that during the return stroke of the actuator piston hydraulic fluid is trapped in the cavity forming a cushion and reducing the velocity of the actuator piston. The upper end of the actuator piston may include a projection section capable of fitting within the cavity. The lower end of the central bore may include a reduced diameter section and the actuator piston includes a projection capable of fitting within the reduced diameter section of the central bore so that during the opening of the engine valve a cushion is formed which limits the movement of the engine valve. The actuator may frtther include a means for adjusting the actuator for variations in engine valve lash. The means for adjusting may comprise: a vertically aligned central passage located within in the actuator piston; an adjustable pin threaded into the central passage projecting downward from the actuator piston to operatively connect with the engine valve; and a locking pin located in the central passage above the adjustable pin to secure the adjustable pin in position.